Ink composition

ABSTRACT

Provided in one example herein is a liquid electrophotographic ink composition. The composition includes a charge director, a non-polar carrier fluid comprising a polymer; and ink particles each including a polymeric resin and a pigment dispersed in the resin. The ink composition also includes a tackifier.

BACKGROUND

One example of digital printing is electrophotographic printing. Liquidelectrophotographic printing, or “LEP,” is a specific type ofelectrophotographic printing, in which a liquid ink (or “LEP ink”),instead of a powder toner, is employed in the electrophotographicprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

The drawings are provided to illustrate various examples of the subjectmatter described herein in this disclosure (hereafter “herein” forshort, unless explicitly stated otherwise) related to a composition forLEP, particularly one that comprises a tackifier, and are not intendedto limit the scope of the subject matter. The drawings are notnecessarily to scale.

FIG. 1 is a schematic flowchart showing the processes involved in oneexample method of manufacturing the ink composition described herein.

FIGS. 2A-2D show, in one example, the peeling tests for ink compositionson the four different substrates (A: Euroart; B: UPM; C: Fortune Matte;and D: Soperset).

FIGS. 3A-3D show, in one example, the peeling tests for ink compositionson the four different substrates (A: Soperset; B: Euroart; C: UPM; and DFortune Matte).

FIGS. 4A-4D show, in one example, optical images of an ink compositioncontaining a tackifier on a (A) new blanket and (B) used blanket.

FIG. 5 shows, in one example, background on blanket (“BOB”) accumulatedink remnants on blanket in non-image areas) vs. stages in a short presstest (20K imp run).

FIGS. 6A-6B show, in one example, optical images of yellow cleaner pagesprinted at 24 stages in order to clean and recover the blanket: FIG. 6Aink composition without a tackifier; and FIG. 6B: ink composition with atackifier.

DETAILED DESCRIPTION

Electrophotographic printing processes, sometimes known as electrostaticprinting processes, may involve creating an image on a photoconductivesurface, applying a printing composition having charged particles to thephotoconductive surface, such that they selectively bind to the image,and then transferring the charged particles in the form of the image toa print substrate.

The photoconductive surface may be on a cylinder and is also known as aphoto imaging plate (“PIP”). The photoconductive surface may beselectively charged with a latent electrostatic image having the imageand the background areas with different potentials. For example, aprinting composition comprising charged toner particles in a carrierfluid may be brought into contact with the selectively chargedphotoconductive surface. The charged toner particles adhere to the imageareas of the latent image while the background areas remain clean. Theimage is then transferred to a print substrate (e.g., paper) directly,or by being first transferred to an intermediate transfer member, whichmay be a soft swelling blanket often heated to fuse the solid image andevaporate the carrier fluid, and then to the print substrate.

To obtain the desirable level of durability of the ink composition,often mechanically strong and high molecular weight resins are employed.However, this type of resin may often encounter the challenge ofadhesion and transferability. Specifically, this type of resin may havea low affinity to the substrate, thus reducing the adhesion of the inkcomposition to the substrate and transferability thereof.

In view of the aforementioned challenges, the Inventors have recognizedand appreciated the advantages of an ink composition described herein.Following below are more detailed descriptions of various examplesrelated to a liquid electrophotographic ink composition, particularlyone comprising a tackifier. The various examples described herein may beimplemented in any of numerous ways.

Provided in one aspect of the examples is a liquid electrophotographicink composition, comprising: a charge director; a non-polar carrierfluid comprising a polymer; and ink particles each comprising apolymeric resin and a pigment dispersed in the resin; and a tackifier.

Provided in another aspect of the examples is a method of manufacturinga liquid electrophotographic ink composition, the method comprising:dissolving a tackifier in a non-polar carrier fluid comprising a polymerto form a mixture; combining the mixture with a charge director and inkparticles each comprising a polymeric resin and a pigment dispersed inthe resin to form the liquid electrophotographic ink composition.

Provided in another aspect of the examples is an article, comprising: asubstrate; an electrophotographic ink composition printed over at leasta portion of the substrate, the electrophotographic ink compositioncomprising: a charge director; a non-polar polymer comprising anisoparaffin; ink particles each comprising a polymeric resin and apigment dispersed in the resin; and a tackifier.

Liquid Electro Photographic Printing

The term “electrostatic ink composition” or “liquid electrophotographiccomposition” herein may refer to an ink composition that is suitable foruse in an electrostatic printing process, also known as an“electrophotographic printing process.” It may comprise ink particles,which may comprise a thermoplastic resin.

The term “copolymer” refers to a polymer that is polymerized from atleast two monomers.

The term “melt flow rate” may refer to the extrusion rate of a resinthrough an orifice of defined dimensions at a specified temperature andload, usually reported as temperature/load, e.g., 190° C./2.16 kg. Flowrates may be used to differentiate grades or provide a measure ofdegradation of a material as a result of molding. “Melt flow rate”herein may refer to that measured per ASTM D1238-04c Standard TestMethod for Melt Flow Rates of Thermoplastics by Extrusion Plastometer.If a melt flow rate of a particular polymer or copolymer is specifiedherein, unless otherwise stated, it refers to the melt flow rate forthat polymer or copolymer alone, in the absence of any of the othercomponents of the LEP printing composition.

The term “acidity,” “acid number,” or “acid value” may refer to the massof potassium hydroxide (KOH) in milligrams that neutralizes one gram ofa substance. The acidity of a polymer or copolymer may be measuredaccording to standard techniques, for example as described in ASTMD1386. If the acidity of a particular polymer or copolymer is specified,unless otherwise stated, it is the acidity for that polymer or copolymeralone, in the absence of any of the other components of the LEP printingcomposition.

The term “melt viscosity” may refer to the ratio of shear stress toshear rate at a given shear stress or shear rate. Testing may beperformed using a capillary rheometer. A plastic charge is heated in therheometer barrel and is forced through a die with a plunger. The plungeris pushed either by a constant force or at constant rate depending onthe equipment. Measurements may be taken once the system has reachedsteady-state operation. One method used is measuring Brookfieldviscosity at 140° C., units are mPa-s or cPoise (“CP”). In anothermethod, the melt viscosity is measured using a rheometer, e.g., acommercially available AR-2000 Rheometer from Thermal AnalysisInstruments, using the geometry of: 25 mm steel plate-standard steelparallel plate, and finding the plate over plate rheometry isotherm at120° C., 0.01 Hz shear rate. If the melt viscosity of a particularpolymer or copolymer is specified, unless otherwise stated, it is themelt viscosity for that polymer or copolymer alone, in the absence ofany of the other components of the LEP printing composition.

When a standard test is mentioned herein, unless otherwise stated, theversion of the test to be referred to is the most recent at the time offiling this patent application.

The term “electrostatic printing” or “electrophotographic printing” mayrefer to the process that provides an image that is transferred from aphoto imaging substrate either directly or indirectly via anintermediate transfer member to a print substrate. As such, the image isat least substantially not absorbed into the photo imaging substrate onwhich it is applied. Additionally, “electrophotographic printers” or“electrostatic printers” generally may refer to those printers capableof performing electrophotographic printing or electrostatic printing asdescribed herein. “Liquid electrophotographic printing” is a specifictype of electrophotographic printing where a liquid composition isemployed in the electrophotographic process rather than a powder toner.An electrostatic printing process may involve subjecting theelectrostatic composition to an electric field, e.g., an electric fieldhaving a field gradient of 50-400 V/μm or more—e.g., 600-900 V/μm ormore.

The term “colored” is used to refer to any color, including white andblack.

The term “colored toner image” refers to an image formed from an LEPink. An LEP ink may contain a pigment.

The indefinite articles “a” and “an,” as used herein in this disclosure,including the claims, unless clearly indicated to the contrary, shouldbe understood to mean “at least one.” Any ranges cited herein areinclusive.

The terms “substantially” and “about” used throughout this disclosureare used to describe and account for small fluctuations. For example,they may refer to less than or equal to ±5%, such as less than or equalto ±2%, such as less than or equal to ±1%, such as less than or equal to±0.5%, such as less than or equal to ±0.2%, such as less than or equalto ±0.1%, such as less than or equal to ±0.05%.

Liquid Electrophotographic Printing Ink Composition

An LEP ink may be any known LEP ink composition comprising a firstpolymeric resin and a second polymeric resin, such as any of thosedescribed herein. The composition may further comprise a carrier fluid.The composition may further comprise a colorant. The composition mayfurther comprise a charge director and/or a charge adjuvant. In oneexample an LEP ink composition may lack a second polymeric resin asdescribed herein. In one example, the LEP ink composition may be HPIndigo's Electroink® 4.5.

To the extent applicable, the terms “first,” “second,” “third,” etc.herein are merely employed to show the respective objects described bythese terms as separate entities and are not meant to connote a sense ofchronological order, unless stated explicitly otherwise herein.

A “melting point” may be measured, and thus defined, herein usingdifferential scanning calorimetry (“DSC”) and may be determined from thefirst heat flow minima reached on heating the polymeric resin from −50°C. at a rate of 15° C./min. The “melting point” of a polymeric resin maybe measured using established standard procedures, for example using theprocedure described ASTM D3418.

The terms “partially molten,” “partially melt,” and “partially melted”are used to refer to an image containing a polymeric resin in which thepolymeric resin has been at least partially melted or softened. This maybe determined as when the resin has become tacky. A polymeric resin maybecome partially molten when heated to a temperature approaching themelting point of the polymeric resin. For example, an (ink) image may beconsidered to be at least partially molten when the image has reached atemperature that is about 20° C. or less below the melting point of thepolymeric resin. In one example, the image is considered to be at leastpartially molten when the image has reached a temperature that is about15° C. or less below the melting point of either the first polymericresin or the second polymeric resin. In one example, the image isconsidered to be at least partially molten when the image has reached atemperature that is about 10° C. or less below the melting point ofeither the first polymeric resin or the second polymeric resin. In oneexample, the image is considered to be at least partially molten whenthe image has reached a temperature that is about 5° C. or less belowthe melting point of either the first polymeric resin or the secondpolymeric resin. In one example, the second polymeric resin has a lowermelting temperature than the first polymeric resin, and thus the frameof reference of “partially molten” is the melting point of the secondpolymeric resin.

In one example, an image is considered to be at least partially moltenwhen the image has been held at a temperature approaching the meltingpoint of either the first or second polymeric resin for at least 0.5seconds, in one example at least 1 second, in one example at least 5seconds, in one example at least 10 seconds

The temperature range at which a first or second polymeric resin willstart to soften or partially melt from data obtained may be determinedby using differential scanning calorimetry (“DSC”) on a resin sampleusing the procedure described in ASTM D3418 showing heat flow to thesample over a temperature range covering the melting point of the resincomponent. A graph showing the heat flow to the sample againsttemperature obtained by DSC may show a broad trough for the meltingpoint of the resin. At temperatures below the melting point of theresin, determined as described above, but still within the broad troughthe resin will be softened or partially molten.

The ink composition described herein may have any color. In one example,the ink composition, particularly the one having a first and a secondpolymeric resins, is transparent.

Ink Particles

The ink composition described herein may comprise any number of suitableconstituents. For example, the ink composition may comprise inkparticles (in some instances known as toner particles) and a carrierfluid in which the ink particles are dispersed. An ink particle may be acomposite comprising at least one polymeric resin (in some instancesknown as a binder), such as a polymeric resin mixture, and a colorant.The colorant may be a dye, pigment particles, etc.

The term “pigment” may refer to pigment colorants, magnetic particles,alumina, silica, and/or other ceramics or organometallics, whether ornot such particulates impart color. In some instances, the term“pigment” may be used more generally to describe not just pigmentcolorants, but other pigments such as organometallics, ferrites,ceramics, etc.

The ink particles are the solid constituents, as opposed to a liquidconstituent (e.g., carrier fluid) of an ink composition. The inkcomposition may also comprise a charge director and/or charge adjuvantdispersed in the carrier fluid. The polymeric resin of the ink particlesmay facilitate the attachment of the charge director(s) to the inkparticles, thereby charging the ink particles.

In one example wherein the ink particles comprise a colorant, thecolorant may be dispersed in a polymeric resin (binder), which maycomprise one polymeric resin or a mixture of multiple polymeric resins.The colorant particles may be distributed in the polymeric resinhomogeneously or inhomogeneously. The polymeric resin may encapsulatethe colorant particles during the production of an LEP ink. The polymerresin may provide structural integrity for an ink film after printing.Depending on the application, the polymeric resin described herein mayrefer to any suitable polymeric resin, such as those described below.

The ink particles may have any suitable geometry. For example, theparticles may be spherical, ellipsoidal, cubical, cylindrical, spiny,wire-like, sheet-like, flake-like, etc. The ink particles may have anirregular geometry. In one example, the ink particles described hereinare spherical. The term “spherical” herein may encompass a shape that isa perfect sphere or almost spherical. The term “almost spherical” mayrefer to a shape that resembles a sphere but is not completelyspherical, such as having a relatively small amount of irregularitydeviating from a perfect spherical shape. Thus, a spherical particleherein may refer to a particle having a sphericity of at least about0.80—e.g., at least about 0.85, about 0.90, about 0.95, or higher. Thepigment particles within the ink particles may also have any suitablegeometry, such as any of the geometries described herein for the inkparticles. The pigment particles may have the same geometry as the inkparticles, or they may have a different geometry from the ink particles.

The ink particles may have any suitable size. Depending on the geometry,the term “size” herein may refer to length, width, height, diameter,etc. Also, when referring to a plurality of objects, the value of any ofthe dimensions described herein may refer to a statistical average. Inone example, the ink particles have an average diameter of between about5 μm and about 80 μm—e.g., between about 10 μm and about 50 μm, betweenabout 15 μm and about 40 μm, between about 20 μm and about 30 μm, etc.

The ink particles may be present in the ink composition at any suitableamount. For example, the ink particles may be present in the inkcomposition at between about 1 wt % and about 50 wt %—e.g., betweenabout 2 wt % and about 40 wt %, between about 3 wt % and about 30 wt %,between about 4 wt % and about 20 wt %, between about 5 wt % and about10 wt %, etc. Other content values are also possible. In one example,the ink particles are present in the ink composition at between about 1wt % and about 10 wt %—e.g., about 2 wt % and about 8 wt %, about 4 wt %and about 6 wt %, etc.

Colorant

The LEP ink composition described herein may or may not comprise acolorant. In one example, the ink composition lacks a colorant. In oneexample, ink composition lacks an inorganic particulate material. In anexample, the ink composition is substantially transparent when printed.

The ink composition may be a substantially colorless, clear, ortransparent compositions substantially free from pigment. The term“substantially free from pigment” herein may refer to an ink compositionin which less than or equal to 1 wt % of the solids in the inkcomposition comprises a colorant—e.g., less than or equal to about 0.5wt %, about 0.1 wt %, about 0.05 wt %, about 0.01 wt %, or less, of thesolids in the ink composition. In examples in which the ink compositionsare substantially free from pigment, they may be used as glosses andgloss inhibitors in the methods described herein without contributing afurther subtractive effect on the CMYK inks that would otherwisesubstantially affect the color of an under-printed colored image.

The ink composition, either before or after having been printed on aprint substrate, may comprise a colorant. The first and/or secondpolymeric resins may further comprise a colorant.

The colorant may be selected from a pigment, dye, or both. The colorantmay be transparent, unicolor, or being any combination of availablecolors. The colorant may be selected from a white colorant, a cyancolorant, a yellow colorant, a magenta colorant and a black colorant.The ink composition may comprise a plurality of colorants. The inkcomposition may comprise a first colorant and second colorant, which aredifferent from one another. Further colorants may also be present withthe first and second colorants. The ink composition may comprise firstand second colorants where each are independently selected from a whitecolorant, a cyan colorant, a yellow colorant, a magenta colorant and ablack colorant. In one example, the first colorant comprises a blackcolorant, and the second colorant comprises a non-black colorant, forexample a colorant selected from a white colorant, a cyan colorant, ayellow colorant and a magenta colorant. The colorant may be selectedfrom a phthalocyanine colorant, an indigold colorant, an indanthronecolorant, a monoazo colorant, a diazo colorant, inorganic salts andcomplexes, dioxazine colorant, perylene colorant, anthraquinonecolorants, and any combination thereof.

The colorant may comprise a pigment. The pigments may be any pigmentcompatible with the liquid carrier and useful for electrostaticprinting. For example, the pigment may be present as pigment particles,or may comprise a resin (in addition to the polymers described herein)and a pigment. The resins and pigments may be any of those commonly usedin the industry. For example, pigments by Hoechst including PermanentYellow DHG, Permanent Yellow GR, Permanent Yellow G, Permanent YellowNCG-71, Permanent Yellow GG, Hansa Yellow RA, Hansa Brilliant Yellow5GX-02, Hansa Yellow X, NOVAPERM® YELLOW HR, NOVAPERM® YELLOW FGL, HansaBrilliant Yellow 10GX, Permanent Yellow G3R-01, HOSTAPERM® YELLOW H4G,HOSTAPERM® YELLOW H3G, HOSTAPERM® ORANGE GR, HOSTAPERM® SCARLET GO,Permanent Rubine F6B; pigments by Sun Chemical including L74-1357Yellow, L75-1331 Yellow, L75-2337 Yellow; pigments by Heubach includingDALAMAR® YELLOW YT-858-D; pigments by Ciba-Geigy including CROMOPHTHAL®YELLOW 3 G, CROMOPHTHAL® YELLOW GR, CROMOPHTHAL® YELLOW 8 G, IRGAZINE®YELLOW 5GT, IRGALITE® RUBINE 4BL, MONASTRAL® MAGENTA, MONASTRAL®SCARLET, MONASTRAL® VIOLET, MONASTRAL® RED, MONASTRAL® VIOLET; pigmentsby BASF including LUMOGEN® LIGHT YELLOW, PALIOGEN® ORANGE, HELIOGEN®BLUE L 690 IF, HELIOGEN® BLUE TBD 7010, HELIOGEN® BLUE K 7090, HELIOGEN®BLUE L 710 IF, HELIOGEN® BLUE L 6470, HELIOGEN® GREEN K 8683, HELIOGEN®GREEN L 9140; pigments by Mobay including QUINDO® MAGENTA, INDOFAST®BRILLIANT SCARLET, QUINDO® RED 6700, QUINDO® RED 6713, INDOFAST® VIOLET;pigments by Cabot including Maroon B STERLING® NS BLACK, STERLING® NSX76, MOGUL® L; pigments by DuPont including TIPURE® R-101; and pigmentsby Paul Uhlich including UHLICH® BK 8200.

The pigment particles in the ink particles may have any suitable size.The size of the pigment particles generally is smaller than that of theink particles. In one example wherein the ink particles comprise verylittle, such as no, polymeric resin, the size of the pigment particlesis about the same as that of the ink particles. In one example, whilethe overall ink particles have the aforementioned average diameters, thepigment particles have an average diameter of between about 50 nm andabout 600 nm—e.g., between about 100 nm and about 300 nm, between about200 nm and about 250 nm, etc. Other diameter values are also possible.

The pigment particles may comprise any suitable material. The type ofmaterial employed may depend on, for example, the color intended for thepigment particles to provide. For example, the material may comprise atleast one ceramic. The ceramic may be a metal oxide. The metal in themetal oxide may be, for example, a transition metal. The metal oxide maycomprise at least one of titanium dioxide, aluminum oxide, and zincoxide. In one example, the metal oxide comprises titanium dioxide. Inone example, the metal oxide is titanium dioxide and the ink compositionis white. In another example, the metal oxide comprises titanium dioxideand the ink composition is not white. Where the pigment is a whitepigment particle, the pigment particle may be selected from the groupconsisting of TiO₂, calcium carbonate, zinc oxide, and mixtures thereof.In one example, the white pigment particle may comprise an alumina-TiO₂pigment. Depending on the application, other types of materials,including other types of metal oxides, may be employed.

The ink particles provided herein may have any suitable level of pigmentloading, depending on the application. The term “pigment loading” mayrefer to the average content of the pigment particles in the inkparticles. The content may refer to volume percentage (“vol %”) orweight percentage (“wt %”), depending on the context. In one example,the pigment loading refers to the average wt % of the pigment particlesin the ink particles. In one example wherein the pigment particlescomprise at least one metal oxide, the “pigment loading” with respect toeach of the at least one metal oxide refers to the average wt % of eachof the at least one metal oxide in the ink particles. In one examplewherein the pigment particles comprise only one type of metal oxide, thepigment loading of the ink particles as a whole refers to the average wt% of this metal oxide in the ink particles. In one example, pigmentloading refers to the average wt % of titanium dioxide in the inkparticles. In one example, the pigment loading of a metal oxide in theink particles is less than or equal to about 60 wt % of the inkparticles, such as less than or equal to about 55 wt %—e.g., less thanor equal to about 50 wt %, about 40 wt %, about 30 wt %, about 20 wt %,or lower. In one example, the pigment loading of a metal oxide in theink particles is between about 8 wt % and about 55 wt %—e.g., betweenabout 9 wt % and about 50 wt %, between about 10 wt % and about 40 wt %,between about 11 wt % and about 30 wt %, between about 12 wt % and about20 wt %, etc. In one example, the pigment loading of a metal oxide inthe ink particles is between about 12 wt % and about 18 wt %. In oneexample, the aforementioned pigment loading refers to that of a whiteink composition. Other pigment loading values are also possible. Forexample, other pigment loading values may be employed for a differentcolor of an ink composition.

Polymeric Resins

The polymeric resin may act as a matrix in which the pigment particlesare dispersed/distributed. The polymeric resin may be any suitablepolymeric resin material or a mixture of different polymeric resinmaterials. The polymeric resin may refer to a synthetic polymeric resinor a natural polymeric resin. The ink composition described herein maycomprise a polymeric mixture of at least two polymeric resins. In oneexample, the polymeric resin has two polymeric resins. In anotherexample, the polymeric resin has only one polymeric resin.

The polymer resin may comprise a thermoplastic polymer. The polymerresin may comprise a copolymer. The polymeric resin may comprisecopolymers of any suitable microstructure. The polymer resin maycomprise a random copolymer. For example, the polymeric resin maycomprise an ethylene-based polymeric resin. For example, the polymericresin may comprise, or be, a random copolymer comprising an ethylene.Examples of suitable ethylene-based polymeric resins comprise copolymersof ethylene, methacrylic acid, and acrylic acid; copolymers of ethyleneand an acrylate; copolymers of ethylene and vinyl acetate; or variouscombinations of these copolymers. When copolymers of ethylene and anacrylate are employed, the acrylate may be a butyl-acrylate, anethyl-acrylate, a methyl-acrylate, or various combinations thereof. Somecommercially available examples of copolymers of ethylene and anacrylate include ELVALOY® AC resins by DuPont Company, USA. Somecommercially available examples of copolymers of ethylene and vinylacetate include ELVAX® resins and BYNEL® resins from DuPont Company,USA.

The polymeric resin may comprise an ethylene acrylic acid resin, anethylene methacrylic acid resin, or a combination thereof. The ethyleneacrylic acid resins and the ethylene methacrylic acid resins may also bedescribed as ethylene acrylic acid copolymers and ethylene methacrylicacid copolymers. In one example, the ethylene acrylic acid resin and theethylene methacrylic acid resin contain 80 wt % to 99.9 wt % of ethyleneand 0.1 wt % to 20 wt % of acrylic or methacrylic acid.

In one example, the polymeric resin has a melting point within the rangeof from about 80° C. to about 120° C., in one example from about 90° C.to about 110° C. In one example, the first polymeric resin has a meltingpoint within the range of from about 80° C. to about 100° C. The meltingpoint of a resin component may be measured using established procedures,for example using the procedure described ASTM D3418.

Ethylene acrylic acid copolymers and ethylene methacrylic acidcopolymers contain acidic side groups. The polymeric resin may containcopolymers having an acidity of 50 mg KOH/g or more, in one example anacidity of 60 mg KOH/g or more, in one example an acidity of 70 mg KOH/gor more, in one example an acidity of 80 mg KOH/g or more, in oneexample an acidity of 90 mg KOH/g or more, in one example an acidity of100 mg KOH/g or more, in one example an acidity of 105 mg KOH/g or more,in one example 110 mg KOH/g or more, in one example 115 mg KOH/g ormore. The polymeric resin containing a resin having acidic side groupsmay have an acidity of 200 mg KOH/g or less, in one example 190 mg orless, in one example 180 mg or less, in one example 130 mg KOH/g orless, in one example 120 mg KOH/g or less. Acidity of a resin, asmeasured in mg KOH/g may be measured using established procedures, forexample using the procedure described in ASTM D1386.

The polymeric resin comprising an ethylene acrylic acid copolymer and/oran ethylene methacrylic acid copolymer having acidic side groups mayhave a melt flow rate of less than about 120 g/10 minutes, in oneexample about 110 g/10 minutes or less, in one example about 100 g/10minutes or less, in one example about 90 g/10 minutes or less, in oneexample about 80 g/10 minutes or less, in one example about 70 g/10minutes or less, in one example about 60 g/10 minutes or less, in oneexample about 50 g/10 minutes or less, in one example about 40 g/10minutes or less, in one example 30 g/10 minutes or less, in one example20 g/10 minutes or less, in one example 10 g/10 minutes or less.

The polymeric resin containing an ethylene acrylic acid copolymer and/oran ethylene methacrylic acid copolymer having acidic side groups, mayhave a melt flow rate of about 10 g/10 minutes to about 120 g/10minutes, in one example about 10 g/10 minutes to about 70 g/10 minutes,in one example about 10 g/10 minutes to 40 g/10 minutes, in one example20 g/10 minutes to 30 g/10 minutes. The ethylene acrylic acid copolymerand/or the ethylene methacrylic acid copolymer having acidic side groupsmay have a melt flow rate of, In one example, about 50 g/10 minutes toabout 120 g/10 minutes, in one example 60 g/10 minutes to about 100 g/10minutes. The melt flow rate may be measured using established standardprocedures, for example as described in ASTM D1238.

The acidic side groups may be in free acid form or may be in the form ofan anion and associated with at least one counterion, such as metalcounterions, e.g., a metal selected from the alkali metals, such aslithium, sodium, and potassium; alkali earth metals, such as magnesiumor calcium; and transition metals, such as zinc. The polymeric resinselected from ethylene acrylic acid resins, ethylene methacrylic acidresins, or combinations thereof may have acidic sides groups which areat least partially neutralized with metal ions (e.g., Zn, Na, and Li)such as SURLYN® ionomers. The ethylene acrylic acid copolymers andethylene methacrylic acid copolymers may be such that either the acrylicor methacrylic acid constitute from 5 wt % to about 25 wt % of theethylene acrylic acid or ethylene methacrylic acid copolymer, in oneexample from 10 wt % to about 20 wt % of the ethylene acrylic acid orethylene methacrylic acid copolymer.

The polymeric resin may comprise two different ethylene acrylic acidand/or ethylene methacrylic acid copolymers having acidic side groups.The two copolymers having acidic side groups may have differentacidities, which may fall within the ranges mentioned above. The resinmay comprise a first copolymer having acidic side groups that has anacidity of from 10 mg KOH/g to 110 mg KOH/g, in one example 20 mg KOH/gto 110 mg KOH/g, in one example 30 mg KOH/g to 110 mg KOH/g, in oneexample 50 mg KOH/g to 110 mg KOH/g, and a second copolymer havingacidic side groups that has an acidity of 110 mg KOH/g to 130 mg KOH/g.In one example, the first copolymer may be NUCREL® 699 (available fromDuPont, USA). In one example, the second copolymer may be A-C® 5120(available from Honeywell, USA).

The ratio of the first copolymer having acidic side groups to the secondcopolymer having acidic side groups may be from about 10:1 to about 2:1.The ratio may be from about 6:1 to about 3:1, in one example about 4:1.

The polymeric resin may comprise an ethylene acrylic acid and/or anethylene methacrylic acid copolymer having a melt viscosity of about15000 poise or less, in one example a melt viscosity of about 10000poise or less, in one example about 1000 poise or less, in one exampleabout 100 poise or less, in one example about 50 poise or less, in oneexample about 10 poise or less; said copolymer may be an ethyleneacrylic acid and/or an ethylene methacrylic acid copolymer having acidicside groups as described herein. The polymeric resin may comprise afirst copolymer having a melt viscosity of about 15000 poise or more, inone example about 20000 poise or more, in one example about 50000 poiseor more, in one example about 70000 poise or more; and In one example,the resin may comprise a second copolymer having a melt viscosity lessthan the first polymer, in one example a melt viscosity of about 15000poise or less, in one example a melt viscosity of about 10000 poise orless, in one example about 1000 poise or less, in one example about 100poise or less, in one example about 50 poise or less, in one exampleabout 10 poise or less. The resin may comprise a first copolymer havinga melt viscosity of more than about 60000 poise, in one example fromabout 60000 poise to about 100000 poise, in one example from about 65000poise to about 85000 poise; a second copolymer having a melt viscosityof from about 15000 poise to about 40000 poise, in one example about20000 poise to about 30000 poise, and a third copolymer having a meltviscosity of about 15000 poise or less, in one example a melt viscosityof about 10000 poise or less, in one example about 1000 poise or less,in one example about 100 poise or less, in one example about 50 poise orless, in one example about 10 poise or less; an example of the firstcopolymer is NUCREL® 960 ((available from DuPont Company, USA), andexample of the second copolymer is NUCREL® 699 (from DuPont Company,USA), and an example of the third copolymer is A-C® 5120 or A-C® 5180(available from Honeywell, USA). The first, second, and third copolymersmay be selected from ethylene acrylic acid and/or ethylene methacrylicacid copolymers having acidic side groups as described herein. The meltviscosity may be measured using a rheometer, e.g., a commerciallyavailable AR-2000 Rheometer from Thermal Analysis Instruments, using thegeometry of: 25 mm steel plate-standard steel parallel plate, andfinding the plate over plate rheometry isotherm at 120° C., 0.01 Hzshear rate.

When the polymeric resin in the ink composition comprises a single typeof ethylene acrylic acid or ethylene methacrylic acid copolymer, thecopolymer (excluding any other components of the ink composition) mayhave a melt viscosity of 6000 poise or more, in one example a meltviscosity of about 8000 poise or more, in one example a melt viscosityof about 10000 poise or more, in one example a melt viscosity of about12000 poise or more. If the polymeric resin comprises a plurality ofethylene acrylic acid and/or ethylene methacrylic acid copolymers, allthe copolymers of the first polymeric resin may together form a mixture(excluding any other components of the ink composition) that has a meltviscosity of about 6000 poise or more, in one example a melt viscosityof about 8000 poise or more, in one example a melt viscosity of about10000 poise or more, in one example a melt viscosity of about 12000poise or more. Melt viscosity may be measured using standard techniques.The melt viscosity may be measured using a rheometer, e.g., acommercially available AR-2000 Rheometer from Thermal AnalysisInstruments, using the geometry of: 25 mm steel plate-standard steelparallel plate, and finding the plate over plate rheometry isotherm at120° C., 0.01 Hz shear rate.

The polymeric resin may comprise two different copolymers having acidicside groups that are selected from copolymers of ethylene and anethylenically unsaturated acid of either acrylic acid or methacrylicacid; or an ionomer of ethylene methacrylic acid copolymer or an ionomerof ethylene acrylic acid copolymer which are at least partiallyneutralized with metal ions (e.g., Zn, Na, Li) such as SURLYN® ionomers.In one example, the polymeric resin comprises a copolymer of ethyleneand methacrylic acid. The polymeric resin may comprise (i) a firstcopolymer that is a copolymer of ethylene and an ethylenicallyunsaturated acid of either acrylic acid and methacrylic acid, whereinthe ethylenically unsaturated acid of either acrylic or methacrylic acidconstitutes from about 8 wt % to about 16 wt % of the copolymer, in oneexample about 10 wt % to about v16 wt % of the copolymer; and (ii) asecond copolymer that is a copolymer of ethylene and an ethylenicallyunsaturated acid of either acrylic acid and methacrylic acid, whereinthe ethylenically unsaturated acid of either acrylic or methacrylic acidconstitutes from about 12 wt % to about 30 wt % of the copolymer, in oneexample from about 14 wt % to about 20 wt % of the copolymer, in oneexample from about 16 wt % to about 20 wt % of the copolymer in oneexample from about 17 wt % to about 19 wt % of the copolymer.

The polymeric resin may comprise an ethylene acrylic acid resin and anethylene methacrylic acid resin. In one example, the ratio by weight ofthe ethylene acrylic acid resin to the ethylene methacrylic acid resinin the first polymeric resin is from about 5:95 to about 30:70.

The polymeric resin may comprise an ethylene acrylic acid and/or anethylene methacrylic acid copolymer having acidic side groups, asdescribed above, and a polymer having ester side groups.

The polymer having ester side groups may be a thermoplastic polymer.

The polymer having ester side groups may further comprise acidic sidegroups. The polymer having ester side groups may be a copolymer of amonomer having ester side groups and a monomer having acidic sidegroups. The polymer may be a copolymer of a monomer having ester sidegroups, a monomer having acidic side groups, and a monomer absent of anyacidic and ester side groups. The monomer having ester side groups maybe a monomer selected from esterified acrylic acid or esterifiedmethacrylic acid. The monomer having acidic side groups may be a monomerselected from acrylic or methacrylic acid. The monomer absent of anyacidic and ester side groups may be an alkylene monomer, including, butnot limited to, ethylene or propylene. The esterified acrylic acid oresterified methacrylic acid may, respectively, be an alkyl ester ofacrylic acid or an alkyl ester of methacrylic acid. The alkyl group inthe alkyl ester of acrylic or methacrylic acid may be an alkyl grouphaving 1 to 30 carbons, in one example 1 to 20 carbons, in one example 1to 10 carbons; in one example selected from methyl, ethyl, iso-propyl,n-propyl, t-butyl, iso-butyl, n-butyl, and pentyl.

The polymer having ester side groups may be a copolymer of a firstmonomer having ester side groups, a second monomer having acidic sidegroups and a third monomer which is an alkylene monomer absent of anyacidic and ester side groups. The polymer having ester side groups maybe a copolymer of (i) a first monomer having ester side groups selectedfrom esterified acrylic acid or esterified methacrylic acid, in oneexample an alkyl ester of acrylic or methacrylic acid; (ii) a secondmonomer having acidic side groups selected from acrylic or methacrylicacid; and (iii) a third monomer which is an alkylene monomer selectedfrom ethylene and propylene. The first monomer may constitute about 1%to about 50% by weight of the copolymer, in one example about 5% toabout 40% by weight, in one example about 5% to about 20% by weight ofthe copolymer, in one example about 5% to about 15% by weight of thecopolymer. The second monomer may constitute about 1% to about 50% byweight of the copolymer, in one example about 5% to about 40% by weightof the copolymer, in one example about 5% to about 20% by weight of thecopolymer, in one example about 5% to about 15% by weight of thecopolymer. The first monomer may constitute about 5% to about 40% byweight of the copolymer, the second monomer constitutes about 5% toabout 40% by weight of the copolymer, and with the third monomerconstituting the remaining weight of the copolymer. In one example, thefirst monomer constitutes about 5% to about 15% by weight of thecopolymer, the second monomer constitutes about 5% to about 15% byweight of the copolymer, with the third monomer constituting theremaining weight of the copolymer. In one example, the first monomerconstitutes about 8% to about 12% by weight of the copolymer, the secondmonomer constitutes about 8% to about 12% by weight of the copolymer,with the third monomer constituting the remaining weight of thecopolymer. In one example, the first monomer constitutes about 10% byweight of the copolymer, the second monomer constitutes about 10% byweight of the copolymer, and with the third monomer constituting theremaining weight of the copolymer. The polymer may be selected from theBYNEL® class of monomer, including BYNEL® 2022 and BYNEL® 2002, whichare available from DuPont Company, USA.

The polymer having ester side groups may constitute about 1% or more byweight of the total amount of the first polymeric resin in the inkcomposition and/or the printing composition printed on the printsubstrate. The polymer having ester side groups may constitute 5 about %or more by weight of the total amount of the first polymeric resinpolymers, in one example about 8% or more by weight of the total amountof the first polymeric resin polymers, in one example about 10% or moreby weight of the total amount of the first polymeric resin polymers, inone example about 15% or more by weight of the total amount of the firstpolymeric resin polymers, in one example about 20% or more by weight ofthe total amount of the first polymeric resin polymers, in one exampleabout 25% or more by weight of the total amount of the first polymericresin polymers, in one example about 30% or more by weight of the totalamount of the first polymeric resin polymers, in one example about 35%or more by weight of the total amount of the first polymeric resinpolymers in the ink composition and/or the ink composition printed onthe print substrate. The polymer having ester side groups may constitutefrom about 5% to about 50% by weight of the total amount of the firstpolymeric resin polymers in the ink composition and/or the inkcomposition printed on the print substrate, in one example about 10% toabout 40% by weight of the total amount of the first polymeric resinpolymers in the ink composition and/or the ink composition printed onthe print substrate, in one example about 5% to about 30% by weight ofthe total amount of the first component resin polymers in the inkcomposition and/or the ink composition printed on the print substrate,in one example about 5% to about 15% by weight of the total amount ofthe first polymeric resin polymers in the ink composition and/or the inkcomposition printed on the print substrate in one example about 15% toabout 30% by weight of the total amount of the first component resinpolymers in the ink composition and/or the ink composition printed onthe print substrate.

The polymer having ester side groups may have an acidity of about 50 mgKOH/g or more, in one example an acidity of about 60 mg KOH/g or more,in one example an acidity of about 70 mg KOH/g or more, in one examplean acidity of about 80 mg KOH/g or more. The polymer having ester sidegroups may have an acidity of 100 mg KOH/g or less, in one example about90 mg KOH/g or less. The polymer having ester side groups may have anacidity of about 60 mg KOH/g to about 90 mg KOH/g, in one example about70 mg KOH/g to about 80 mg KOH/g.

The polymer having ester side groups may have a melt flow rate of about10 g/10 minutes to about 120 g/10 minutes, in one example about 10 g/10minutes to about 50 g/10 minutes, in one example about 20 g/10 minutesto about 40 g/10 minutes, in one example about 25 g/10 minutes to about35 g/10 minutes.

The polymeric resin may comprise copolymers of any suitable materialchemistry. In one example, the polymeric resin comprises ethylene acidcopolymers; ethylene acrylic acid copolymers; methacrylic acidcopolymers; ethylene vinyl acetate copolymers; copolymers of ethyleneacid and alkyls, acrylic acid and alkyls, methacrylic acid and alkyls(with carbon chain lengths between 1 and 20 carbons, inclusive); estersof methacrylic acid or acrylic acid; polyethylene; polystyrene;isotactic polypropylene (crystalline); ethylene ethyl acrylate;polyesters; polyvinyl toluene; polyamides; styrene/butadiene copolymers;epoxy resins; acrylic resins (e.g., copolymer of acrylic or methacrylicacid and at least one alkyl ester of acrylic or methacrylic acid wherethe alkyl is from 1 to about 20 carbon atoms, such as methylmethacrylate or ethylhexylacrylate); ethylene-acrylate terpolymers;ethylene-acrylic esters; maleic anhydride (“MAH”) or glycidylmethacrylate (“GMA”) terpolymers; low molecular weight ethylene-acrylicacid ionomers (i.e., those having a molecular weight of less than about1000 amu); or combinations thereof. In one example, the polymer resincomprises at least one of the NUCREL® or BYNEL® family of polymers(available from DuPont Company, Wilmington, Del., USA)—e.g., NUCREL®403, NUCREL® 407, NUCREL® 609HS, NUCREL® 908HS, NUCREL® 1202HC, NUCREL®30707, NUCREL® 1214, NUCREL® 903, NUCREL® 3990, NUCREL® 910, NUCREL®925, NUCREL® 609, NUCREL® 599, NUCREL® 699, NUCREL® 960, NUCREL® RX 76,NUCREL® 2806; BYNEL® 2002, BYNEL® 2014, or BYNEL® 2020; the ACLYN®family of polymers (available from Honeywell International, Inc.,Morristown, N.J. USA)—e.g., ACLYN® 201, ACLYN® 246, ACLYN® 285, orACLYN® 295; or the LOTADER® family of polymers (available from Arkema,Inc., King of Prussia, Pa., USA)—e.g., LOTADER® 2210, LOTADER® 3430, orLOTADER® 8200. Another example of suitable polymeric resins is A-C®family of resins, such as A-C® 5120, available from Honeywell, USA. Thepolymeric resin may have at least one functional group, such ascarboxylic acid, ester, amide, amine, urea, anhydride, aromatic, orhalogen based groups. Any of the polymeric resins described herein maybe used alone or in combination.

The polymeric resin may be of any content value in the ink particles,depending on the application. For example, the polymeric resin may begreater than about 40 wt % of the ink particles, such as greater than orequal to about 45 wt %—e.g., greater than or equal to about 50 wt %,about 60 wt %, about 70 wt %, about 80 wt %, or higher.

Charge Director & Charge Adjuvant

The ink composition described herein may comprise a charge director. Tobe employed in an LEP application, the ink particles may be charged, forexample, before the particles are incorporated into a toner. Thecharging may involve using at least one charge director. The chargedirector may be added to an ink composition or an electrostatic ink inorder to impart and/or maintain sufficient electrostatic charge onparticles within the ink composition or the electrostatic ink. Thecharge director may also be employed in an LEP ink to preventundesirable aggregation of the ink particles in a carrier fluid. Thecharge director may be a natural charge director (“NCD”) or a syntheticcharge director (“SCD”). For example, the charge director may be a basiccharge director, an acidic charge director, or a neutral chargedirector. The term “charge director” may refer to a material that, whenemployed, facilitates charging of the ink particles, thereby enhancingthe electrophoretic mobility of the ink particles during an LEP. In oneexample, the charge director is basic, which basic charge director mayreact with an acid-modified ink particle to charge negatively theparticle. In other words, the charging of the particle may beaccomplished using an acid-base reaction (or interaction) between thecharge director and the acid-modified particle surface. In anotherexample, the charge director is acidic, which acidic charge director mayreact (or interact) with the base-modified ink particle to chargepositively the particle. The charging of the pigment particle may beaccomplished via an acid-base reaction (or interaction) between thecharge director and the base-modified particle surface. In one example,the charge director is an overall neutral charge director, having anoverall net charge of zero.

The charge director may comprise small molecules or polymers that arecapable of forming reverse micelles in a non-polar carrier fluid. Such acharge director may be colorless and may tend to be dispersible orsoluble in the carrier fluid. The charge director may comprise a neutraland non-dissociable monomer or polymer, such as, for example, apolyisobutylene succinimide amine, which in one example has a molecularstructure as follows:

where “n” is an integer ranging from 15 to 100.

The charge director may be selected from ionic compounds, such as metalsalts of fatty acids, metal salts of sulfosuccinates, metal salts ofoxyphosphates, metal salts of alkyl-benzenesulfonic acid, metal salts ofaromatic carboxylic acids or sulfonic acids, as well as zwitterionic andnon-ionic compounds, such as polyoxyethylated alkylamines, lecithin,polyvinylpyrrolidone, organic acid esters of polyvalent alcohols, etc.For example, the charge director may comprise, or be, at least one of alecithin, a sulfonate salt, and a sulfosuccinate salt. One example of acharge director includes an ionizable molecule that is capable ofdisassociating to form charges. Examples of such a charge directorinclude a metal salt of dialkyl sulfosuccinate, sodiumdi-2-ethylhexylsulfosuccinate or dioctyl sulfosuccinate. In one example,the molecular structure of dioctyl sulfosuccinate is as follows:

In one example, the charge director is selected from, but is not limitedto, oil-soluble petroleum sulfonates (e.g., neutral Calcium Petronate™,neutral Barium Petronate™, and basic Barium Petronate™), polybutylenesuccinimides (e.g., OLOA™ 1200 and Amoco 575), and glyceride salts(e.g., sodium salts of phosphated mono- and diglycerides withunsaturated and saturated acid substituents), sulfonic acid saltsincluding, but not limited to, barium, sodium, calcium, and aluminumsalts of a sulfonic acid. The sulfonic acids may include, but are notlimited to, alkyl sulfonic acids, aryl sulfonic acids, and sulfonicacids of alkyl succinates. In one example, the charge director imparts anegative charge on the particles of the ink composition or the particlesof an electrostatic ink. In one example, the charge director imparts apositive charge on the particles of the ink composition or the particlesof an electrostatic ink. In one example, the charge director comprises aphospholipid, in one example a salt or an alcohol of a phospholipid. Inone example, the charge director comprises species selected from aphosphatidylcholine and derivatives thereof.

The charge director may be a commercially available product. Forexample, the charge director may be an HP Imaging Agent™ (of the HPImaging Agent™ series) commercially available from Hewlett-PackardCompany. The charge director may comprise a sulfosuccinate-containingmolecule. For example, the charge director may comprise (a)nanoparticles of a simple salt; and (b) a sulfosuccinate salt of thegeneral formula MA_(n), wherein M is a metal, n is the valence of M, andA is an ion of the general formula (I): [R₁—O—C(O)CH₂CH(SO₃⁻)C(O)—O—R₂], wherein each of R₁ and R₂ is an alkyl group. In thisexample, the charge director material is substantially free of acids ofthe general formula (I), wherein one or both of R₁ and R₂ is hydrogen,and if only one of them is hydrogen, the other is an alkyl group. Thecharge director may comprise (a) nanoparticles of a simple salt; (b) afirst micelle forming substance, being sulfosuccinate salt of thegeneral formula MA_(n), wherein M is a metal, n is the valence of M, andA is an ion of the general formula (I): [R₁—O—C(O)CH₂CH(SO₃⁻)C(O)—O—R₂], wherein each of R₁ and R₂ is an alkyl group; and (c) asecond micelle forming substance. The aforementioned simple salt maycomprise a cation that is Mg⁺², Ca⁺², Ba⁺², NH₄ ⁺, tert-butyl ammonium,Li⁺, and Al⁺³, or from any sub-group thereof. The aforementioned simplesalt may comprise an anion that is SO₄ ⁻², PO₄ ⁻³, NO₃ ⁻, HPO₄ ⁻², CO₃⁻², acetate, trifluoroacetate (TFA), Cl⁻, Br⁻, I⁻, ClO₄ ⁻, and TiO₃ ⁻⁴,or from any sub-group thereof. For example, the salt may comprise CaCO₃,Ba₂TiO₃, Al₂(SO₄)₃, Al(NO₃)₃, Ca₃(PO4)₂, BaSO₄, BaHPO₄, Ba₂(PO₄)₃,CaSO₄, (NH₄)₂CO₃, (NH₄)₂SO₄, NH₄OAc, tert-butyl ammonium bromide,NH₄NO₃, LiTFA, Al₂(SO₄)₃, LiClO₄ and LiBF₄, or any sub-group thereof.

Another example of a charge director includes a zwitterion chargedirector such as, for example, lecithin (e.g., soya lecithin). Themolecular structure of lecithin is shown as follows:

Other suitable charge directors may also be employed.

Another example of a charge director is a sulfonate salt. The sulfonatesalt may be, for example, a barium sulfonate salt, such as basic bariumpetronate (“BBP”). In one example, basic barium petronate is a bariumsulfonate salt of a 21-26 hydrocarbon alkyl. The sulfonate salt may bean amine salt, such as an isopropyl amine sulfonate salt (which is alsoa sulfonate salt). In one example, isopropyl amine sulfonate salt isdodecyl benzene sulfonic acid isopropyl amine.

The aforedescribed charge directors may be employed in any combination.For example, a combination of lecithin, barium sulfonate salt, andisopropyl amine sulfonate salt may be used. The charge director(s) maybe present in the ink composition at any suitable amount. For example,the charge director may constitute about 0.001% to 20%, in one example0.01% to 20% by weight, in one example about 0.01 to about 10% byweight, in one example about 0.01% to about 1% by weight of the solidsof an ink composition described herein. In one example, the chargedirector constitutes about 0.001% to about 0.15% by weight of the solidsof the ink composition, in one example about 0.001% to about 0.15%, inone example about 0.001% to about 0.02% by weight of the solids of anink composition described herein, in one example about 0.1% to about 2%by weight of the solids of the ink composition, in one example about0.2% to about 1.5% by weight of the solids of the ink composition, inone example about 0.1% to about 1% by weight of the solids of the inkcomposition, in one example about 0.2% to about 0.8% by weight of thesolids of the ink composition. For example, the charge director may bepresent at an amount of at least about 1 mg of charge director per gramof solids of the electrostatic ink composition (which will beabbreviated to mg/g)—e.g., at least about 2 mg/g, about 5 mg/g, about 10mg/g, about 15 mg/g, about 20 mg/g, about 25 mg/g, about 50 mg/g, about60 mg/g, about 80 mg/g, about 100 mg/g, or more. Other values are alsopossible.

In addition to at least one charge director, the ink compositiondescribed herein may also comprise at least one charge adjuvant. Acharge adjuvant sometimes is known as a “grinding aid.” It is noted thatthe types of charge director and charge adjuvant, for the purposes ofthis disclosure, constitute a pigment.

A charge adjuvant may promote charging of the particles when a chargedirector is present. The charge adjuvant may comprise, but is notlimited to, barium petronate, calcium petronate, Co salts of naphthenicacid, Ca salts of naphthenic acid, Cu salts of naphthenic acid, Mn saltsof naphthenic acid, Ni salts of naphthenic acid, Zn salts of naphthenicacid, Fe salts of naphthenic acid, Ba salts of stearic acid, Co salts ofstearic acid, Pb salts of stearic acid, Zn salts of stearic acid, Alsalts of stearic acid, Zn salts of stearic acid, Cu salts of stearicacid, Pb salts of stearic acid, Fe salts of stearic acid, metalcarboxylates (e.g., Al tristearate, Al octanoate, Li heptanoate, Festearate, Fe distearate, Ba stearate, Cr stearate, Mg octanoate, Castearate, Fe naphthenate, Zn naphthenate, Mn heptanoate, Zn heptanoate,Ba octanoate, Al octanoate, Co octanoate, Mn octanoate, and Znoctanoate), Co lineolates, Mn lineolates, Pb lineolates, Zn lineolates,Ca oleates, Co oleates, Zn palmirate, Ca resinates, Co resinates, Mnresinates, Pb resinates, Zn resinates, AB diblock copolymers of2-ethylhexyl methacrylate-co-methacrylic acid calcium and ammoniumsalts, copolymers of an alkyl acrylamidoglycolate alkyl ether (e.g.,methyl acrylamidoglycolate methyl ether-co-vinyl acetate), and hydroxybis(3,5-di-tert-butyl salicylic) aluminate monohydrate. In one example,the charge adjuvant is aluminum di or tristearate.

The charge adjuvant may be present at an amount of about 0.1 to about 5%by weight, in one example about 0.1 to about 1% by weight, in oneexample about 0.3 to about 0.8% by weight of the solids of the inkcomposition, in one example about 1 wt % to about 3 wt % of the solidsof the ink composition, in one example about 1.5 wt % to about 2.5 wt %of the solids of the ink composition.

In one example, the ink composition further comprises, e.g., as a chargeadjuvant, a salt of multivalent cation and a fatty acid anion. The saltof multivalent cation and a fatty acid anion may act as a chargeadjuvant. The multivalent cation may, in one example, be a divalent or atrivalent cation. In one example, the multivalent cation is selectedfrom Group 2, transition metals and Group 3 and Group 4 in the PeriodicTable. In one example, the multivalent cation comprises a metal selectedfrom Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, and Pb. In oneexample, the multivalent cation is Al³⁺. The fatty acid anion may beselected from a saturated or unsaturated fatty acid anion. The fattyacid anion may be selected from a C₈ to C₂₆ fatty acid anion, in oneexample a C₁₄ to C₂₂ fatty acid anion, in one example a C₁₆ to C₂₀ fattyacid anion, in one example a C₁₇, C₁₈, or C₁₉ fatty acid anion. In oneexample, the fatty acid anion is selected from a caprylic acid anion,capric acid anion, lauric acid anion, myristic acid anion, palmitic acidanion, stearic acid anion, arachidic acid anion, behenic acid anion, andcerotic acid anion.

The charge adjuvant, which may, for example, be or comprise a salt ofmultivalent cation and a fatty acid anion, may be present at an amountof 0.1 wt % to about 5 wt % of the solids of the ink composition, in oneexample in an amount of about 0.1 wt % to about 2 wt % of the solids ofthe ink composition, in one example in an amount of about 0.1 wt % toabout 2 wt % of the solids of the ink composition, in one example in anamount of about 0.3 wt % to about 1.5 wt % of the solids of the inkcomposition, in one example about 0.5 wt % to about 1.2 wt % of thesolids of the ink composition, in one example about 0.8 wt % to about 1wt % of the solids of the ink composition, in one example about 1 wt %to about 3 wt % of the solids of the ink composition, in one exampleabout 1.5 wt % to about 2.5 wt % of the solids of the ink composition.

Carrier Fluid

One constituent of the ink composition described herein may be a carrierfluid. The term “carrier fluid” may refer to a fluid in which the inkparticles, including the first and second polymeric resins, aredispersed to form an ink dispersion. In one example, the carrier fluidacts as a dispersing medium for the other constituents, such as the inkparticles, in an ink composition. A carrier fluid may be formulated forelectrophotographic printing such that the electrophotographic ink has aviscosity and conductivity suitable for such printing. The carrier fluidmay be non-polar and substantially non-aqueous—e.g., containing lessthan about 0.5 wt % water. In another example, the hydrocarbon may benon-aqueous—i.e., containing no water. The carrier fluid may comprise atleast one additive, such as surfactants, organic solvents, chargecontrol agents, charge directors, viscosity modifiers, stabilizingagents, anti-kogation agents, etc.

The carrier fluid may comprise, or be, a non-polar carrier. Thenon-polar carrier of the carrier fluid may be the same non-polar carrieremployed throughout the process of forming an ink slurry and/or thefinal ink composition. The carrier fluid may have a differentcomposition from that of the polymeric resin. A non-polar fluid mayrefer to a fluid that has properties such as low odor, lack of color,selective solvency, oxidation stability, low electrical conductivity,low surface tension, desirable wetting, spreadability, low viscosity,narrow boiling point range, non-corrosive to metals, low freezing point,high electrical resistivity, high interfacial tension, low latent heatof vaporization, and low photochemical reactivity.

The carrier fluid may comprise or be a hydrocarbon, silicone oil,vegetable oil, etc. The carrier fluid may comprise, but is not limitedto, an insulating, non-polar, non-aqueous liquid that may be used as amedium for the first and second polymeric resins of the ink particles.The carrier fluid may comprise compounds that have a resistivity inexcess of about 10⁹ ohm-cm. The carrier fluid may have a dielectricconstant below about 5, in one example below about 3. The carrier fluidmay comprise, but is not limited to, hydrocarbons. The hydrocarbon maycomprise, but is not limited to, an aliphatic hydrocarbon, an isomerizedaliphatic hydrocarbon, branched chain aliphatic hydrocarbons, aromatichydrocarbons, and combinations thereof.

Examples of non-polar carriers comprise dielectric liquids,non-oxidative water immiscible liquids (e.g., petroleum distillates),hydrocarbon-based carriers (e.g., aliphatic (i.e., linear/acyclic orcyclic) hydrocarbons, branched-chain aliphatic hydrocarbons, etc.),silicone oil, soy bean oil, vegetable oil, plant extracts, etc. In oneexample, the non-polar carrier is an alkane or a cycloalkane having from6 to 14 carbon atoms (e.g., n-hexanes, heptanes, octane, dodecane,cyclohexane etc.), t-butylbenzene, 2,2,4-trimethylpentane, orcombinations thereof. Examples of a non-polar carrier fluid comprise atleast one substituted or unsubstituted hydrocarbon. The hydrocarbon maybe linear, cyclic, or branched, and may be substituted with any suitablefunctional group. Examples of such hydrocarbons comprise any ofdielectric liquids, non-oxidative water immiscible liquids, paraffins,isoparaffins, and oils. Examples of paraffins and isoparaffins comprisethose in the ISOPAR® family (Exxon Mobil Corporation, USA), including,for example, ISOPAR®-G, ISOPAR®-H, ISOPAR®-K, ISOPAR®-L, ISOPAR®-M, andISOPAR®-V. Additional examples of a suitable carrier fluid includeNORPAR 13™, NORPAR 15™, Exxol D40™, Exxol D80™, Exxol D100™, ExxolD130™, and Exxol D140™, also available from Exxon Mobil Corporation,USA. Some additional examples of a suitable carrier fluid include TeclenN-16™, Teclen N-20™, Teclen N-22™, Nisseki Naphthesol L™, NissekiNaphthesol M™, Nisseki Naphthesol H™, #0 Solvent L™, #0 Solvent M™, #0Solvent H™, Nisseki Isosol 300™, Nisseki Isosol 400™, AF-4™, AF-5™,AF-6™ and AF-7™ (each available from NIPPON OIL CORPORATION); IP Solvent1620™ and IP Solvent 2028™ (each sold by IDEMITSU PETROCHEMICAL CO.,LTD.); Amsco OMS™ and Amsco 460™ (each sold by AMERICAN MINERAL SPIRITSCORP.); and Electron, Positron, New II, Purogen HF (100% syntheticterpenes) (sold by ECOLINK™). In other examples of a suitable carrierfluid, other hydrocarbons that may be used as the non-polar carrierfluid comprise those in the SOLTROL® family (available from ChevronPhillips Chemical Company, USA) or SHELLSOL® (available from ShellChemicals, USA).

In one example, the non-polar carrier fluid comprises any of linear,branched, and cyclic alkanes having from about 6 to about 100 carbonatoms, inclusive; hydrocarbons having from 6 to 14 carbon atoms,inclusive; cycloalkanes having from 6 to 14 carbon atoms, inclusive(e.g., n-hexanes, heptanes, octane, dodecane, cyclohexane, etc.);t-butylbenzene; 2,2,4-trimethylpentane; isoparaffinic hydrocarbons;paraffinic hydrocarbons; aliphatic hydrocarbons; de-aromatizedhydrocarbons; halogenated hydrocarbons; cyclic hydrocarbons;functionalized hydrocarbons; or combinations thereof. The hydrocarbonmay comprise oils, examples of which may comprise, silicone oil, soybean oil, vegetable oil, plant extracts, or combinations thereof. Thehydrocarbon comprised in the non-polar carrier fluid may besubstantially non-aqueous—i.e., comprising less than about 1 wt %water—e.g., less than about 0.5 wt %, about 0.2 wt %, or lower. In oneexample, the hydrocarbon comprises no water. Any of the carrier fluidsdescribed herein may be used alone or in combination.

The carrier fluid may constitute about 20% to about 99.5% by weight ofthe ink composition, in one example about 50% to about 99.5% by weightof the ink composition. The carrier fluid may constitute about 40 toabout 90% by weight of the ink composition. The carrier fluid mayconstitute about 60% to about 80% by weight of the ink composition. Thecarrier fluid may constitute about 90% to about 99.5% by weight of theink composition, in one example about 95% to about 99% by weight of theink composition.

The ink composition described herein, when printed on a print substrate,may be substantially free from carrier fluid—the printed composition isdescribed further below. In an electrostatic printing process and/orafterwards, the carrier fluid may be removed, e.g., by anelectrophoresis processes during printing and/or evaporation, such thatsubstantially just solids are transferred to the print substrate.Substantially free from carrier fluid may indicate that the inkcomposition printed on the print substrate contains less than about 5 wt% carrier fluid, in one example, less than about 2 wt % carrier fluid,in one example less than about 1 wt % carrier fluid, in one example lessthan about 0.5 wt % carrier fluid. In one example, the printingcomposition printed on the print substrate is free from carrier fluid.

Tackifiers

The ink composition described herein may comprise at least onetackifier. In one example, tackifiers are chemical compounds that may beemployed in formulating adhesives to increase the tack, the stickinessof the surface of the adhesive. They may be low-molecular weightcompounds with high glass transition temperature. In one example, at lowstrain rates they provide higher stress compliance and become stiffer athigher strain rates. Tackifiers may have a low molecular weight, andglass transition and softening temperature above room temperature,providing them with suitable viscoelastic properties.

The tackifier described herein may comprise a polymer that has arelatively low molecular weight. For example, the molecular weight Mnmay be between about 400 and about 5000—e.g., between about 500 andabout 3000, between about 600 and about 1000, between about 700 andabout 800, etc. Other values are also possible.

The tackifier described herein may also have a softening temperaturethat is above room temperature. The softening temperature may besufficient to allow the tackifier to be soft and flow on the blanket—inone example allowing for the possibility of film forming. For example,the softening temperature of the tackifier may be between about 50° C.and about 300° C.—e.g., between about 60° C. and about 250° C., betweenabout 70° C. and about 200° C., between about 80° C. and about 150° C.,between about 90° C. and about 120° C., etc. Other values are alsopossible. In one example, the softening temperature is about 100° C.

The tackifier described herein may have a relatively high polarity. Inone example, the polarity is sufficiently high to achieve repulsion fromthe blanket and/or better compatibility with the substrate. The polarityof the tackifier may be reflected in the functional group of the polymerthereof. For example, the tackifier may have a polar functional group,such as a polar acid group. Not to be bound by any particular theory,but due at least in part to its polarity, the tackifier described hereinmay have a relatively high solubility in the non-polar carrier fluid.The carrier fluid may be any of those described here (e.g., isoparaffin,such as Isopar®). In one example, the tackifier described herein may bedissolved in the non-polar carrier fluid completely. A completedissolution herein may encompass a minute variation—e.g., at least 95%dissolution, such as 98%, 99%, 99.5%, or higher, dissolution. Thepercentage may refer to volume or weight, depending on the context.

The tackifier described herein may have any suitable chemistry. Forexample, the tackifier may comprise, or be, resins. For example, thetackifier may comprise, or be, rosins and their derivatives, terpenesand modified terpenes, aliphatic, cycloaliphatic and aromatic resins (C5aliphatic resins, C9 aromatic resins, and C5/C9 aliphatic/aromaticresins), hydrogenated hydrocarbon resins, and their mixtures,terpene-phenol resins (TPR, used often with ethylene-vinyl acetateadhesives). In one example, the tackifier comprises at least one of ahydrocarbon resin, a hydrogenated hydrocarbon resin, a dimerized acidrosin, a terpene phenolic resin, an abietic acid, a rosin ester, and apolyterpene.

The tackifier described herein may be commercially available products.For example, the tackifier may be of the Regalite™ family and theDymerex™ family, availably by Eastman Chemical Company, USA. Forexample, the tackifier may be Regalite™ S 5100, Regalite™ R 1100, etc.In one example, the tackifier comprises, or is, a dimerized acid rosin,such as the Dymerex™ popolymerized rosin. For example, the tackifier maybe of the Sylvares™ family and the Sylvatac™ family, availably byArizona Chemical, USA. For example, the tackifier may be Sylvares™TP-105, Sylvares™ TRB115, Sylvatac™ RE 95, etc. For example, thetackifier may be of the Nures™ family, available by Newport Industries,USA. For example, the tackifier is Nures™ TP100. In one example, TP100comprises a terpene phenolic resin, an abietic acid, and a rosin ester.Other tackifiers are also possible.

Not to be bound by any particular theory, but the increasing chemistrycompatibility of the tackifier to the substrate may enhance imagetransfer to the substrate and enhance incompatibility of the image tothe silicone based releasing surface of the blanket. As a result, thismay enhance the transfer of the image from the blanket to the substrate.

Other Additives

The ink composition may comprise an additive or a plurality ofadditives. The additive or plurality of additives may be added at anystage of producing the ink composition. The additive or plurality ofadditives may be selected from a wax, a surfactant, biocides, organicsolvents, viscosity modifiers, materials for pH adjustment, sequesteringagents, preservatives, compatibility additives, emulsifiers, and thelike. The wax may be an incompatible wax. The term “incompatible wax”may refer to a wax that is incompatible with the resin. Specifically,the wax phase separates from the resin phase upon the cooling of theresin fused mixture on a print substrate during and after the transferof the ink composition to a print substrate during printing of the inkcomposition.

Making/Using the Ink Composition

Electrophotographic printing techniques may involve the formation of alatent image on a photoconductor surface mounted on an imaging plate. Inone example, the photoconductor may first be sensitized to light, in oneexample through charging with a corona discharge, and then may beexposed to light projected through a positive film of the document to bereproduced. This may result in dissipation of the charge in the exposedareas and the formation of a latent image on the photoconductor. Thelatent image may subsequently be developed into a full image by theattraction of oppositely charged toner particles to the charge remainingon the unexposed areas. Next, the developed image may be transferredfrom the photoconductor to the blanket, which in one example is afabric-reinforced sheet of rubber or polymer wrapped around a cylinderwhich may receive the toner from the photoconductor before it istransferred to the substrate. From the blanket, the image may betransferred to organic or inorganic substrates, such as paper, plasticor other suitable materials, by heat, pressure, a combination thereof,or any other suitable method, to produce the printed final image.

FIG. 1 is flowchart showing the processes involved in one example of amethod of manufacturing the LEP ink composition described herein. Themethod may comprise dissolving a tackifier in a non-polar carrier fluidcomprising a polymer to form a mixture (S101). The tackifier andnon-polar carrier fluid may be any of those described herein. Thetackifier may be dissolved at any suitable concentration. For example,the tackifier may be dissolved in the fluid at less than or equal toabout 10%—e.g., between about 0% and about 10%, between about 2% andabout 8%, between about 4% and about 6%, etc. In one example, theconcentration is between about 1% and about 5%. The percentage hereinmay refer to volume or weight percentage, depending on the context. Inone example, the percentage refers to weight %.

The method may further comprise combining the mixture with a chargedirector and ink particles each comprising a polymeric resin and apigment dispersed in the resin to form the liquid electrophotographicink composition (S102). The charge director and ink particles may be anyof those described herein.

The method as described in FIG. 1 may further comprise using themanufactured ink composition in a printing process. The printing processmay involving using any of the printers described above. The printingprocess may comprise disposing the liquid electrophotographic inkcomposition over a portion of a substrate. The printing process mayfurther comprise drying the disposed liquid electrophotographic inkcomposition to form an image over the portion. The drying process mayinvolve application of heat and/or pressure.

In one example, the ink composition containing at least one tackifierdescribed herein exhibits tackifying characteristic. For example, theink composition may adhere the dried image thin film to the substratewith better peeling results (than an ink without a tackifier). Inaddition, most of the tackifier materials may be relatively polar,therefore the polar groups may reject from the hydrophobic blanket andimprove adhesion to the hydrophilic substrate.

The ink composition may be fabricated by combining at least inkparticles, such as any of those described herein, a charge director,such as any of those described herein, and at least a carrier fluid,such as any of those described herein. Depending on the application, theink composition may be fabricated by incorporating additionalconstituents, such as at least one additive, including, for example,surfactants, organic solvents, charge control agents, viscositymodifiers, stabilizing agents, and anti-kogation agents. In one example,the additives comprise at least one of charge control agents,dispersants, plasticizers, polymers, resins, theology modifiers, salts,stabilizers, surfactants, UV curable materials, viscosity modifiers, andsurface-active agents. The additives may be present at between about 0wt % and about 10 wt % of the ink composition; other values are alsopossible.

Additionally, the method may further comprise adding an amount of acarrier fluid to adjust the concentration of the ink particles so thatthe ink particles are present in the ink composition at a desirablecontent value, such as those described above. For example, the processof fabricating the ink composition may comprise making any of the inkcomposition constituents, including the ink particles, such as any ofthe ink particles described herein. In one example, the method of makingthe ink particles comprises extruding the raw materials to form anextrudant, cooling the extrudant, and forming the cooled extrudant toform the ink particles.

The raw materials may comprise any suitable material that may beemployed to make the ink particles. For example, the raw materials maycomprise at least one ceramic. The ceramic may be a composite. Theceramic may comprise at least one metal oxide, such as any of the metaloxides described herein. In one example, the at least one metal oxidecomprises titanium dioxide. In another example, the at least one metaloxide comprises multiple types of metal oxides, including at least oneof titanium dioxide, aluminum oxide, and zinc oxide. The raw materialsmay comprise the polymeric resins described herein. In one example, thepolymeric resin comprises a mixture of a polyethylene acrylic acid resinand polyethylene methacrylic acid resin (as the first polymeric resin)and a second polymeric resin. The raw materials may comprise at leastone charge director, such as any of the charge directors describedherein. In one example, the charge director is a natural chargedirector.

The polymeric resin mixture may be melted before the addition of themetal oxide into the molten resin mixture to form an extrudant; or theresin may be melted together with (i.e., in the presence of) the metaloxide. In one example, at least one polymer resin is melted before theat least one metal oxide is incorporated into the molten resin.

Depending on the application, including the materials involved, theextrusion may involve any extrusion suitable for a polymeric material.For example, the extrusion may involve a plastic/polymer extrusion. Theextrusion may be, for example, hot extrusion, warm extrusion, coldextrusion, etc. The extrusion may be, for example, blown film extrusion,sheet/film extrusion, tubing extrusion, over-jacketing extrusion,co-extrusion, etc. Depending on at least the materials involved, theextrusion may involve any suitable processing conditions, includingrotation speed and temperature. For example, the extrusion may involve arotation speed of at least about 50 rpm—e.g., at least about 100 rpm,about 150 rpm, about 200 rpm, about 250 rpm, about 300 rpm, or more.Other values are also possible. For example, the extrusion may involvean extrusion temperature of at least about 60° C.—e.g., at least about80° C., about 100° C., about 120° C., about 140° C., about 160° C.,about 180° C., about 200° C., or higher. Other values are also possible.The temperature profile of the extrusion condition may comprise atemperature profile varying with time, such as a ramp up and/or downprofile.

The extrudant may be cooled to allow for further processing. The coolingmay involve any suitable process to lower the temperature of theextrudant from one temperature to another lower temperature. The lowertemperature may be any suitable temperature, such as room temperature.For example, the cooling may involve a bath, such as a water bath. Afterthe extrudant is cooled, the cooled extrudant may undergo additionalprocessing, including reducing the size of the extrudant. The sizereduction may involve any suitable process. For example, the cooledextrudant may be formed into pellets. The pellets may have any geometry.In one example, the pellets are cylindrical. In one example, the pelletshave an average diameter of about 0.5 mm and about 10 mm—e.g., about 1mm and about 8 mm, about 2 mm and about 6 mm, about 3 mm and about 4 mm,etc. In one example, the pellets have an average length of about 0.1 mmand about 2 mm—e.g., about 0.2 mm and about 1.6 mm, about 0.4 mm andabout 1.2 mm, about 0.6 mm and about 0.8 mm, etc. Other average diameterand length values are also possible.

The pellets may be further processed, such as to further reduce the sizethereof. This further size reduction may involve any suitable process,depending on the application, such as the materials involved. Examplesof the size reduction process may comprise at least one of grinding,precipitation, homogenization, microfluidization, and the like. Thegrinding may involve, for example, milling. The milling may be, forexample, ball milling. Depending on the application, such as thematerials involved, any suitable grinding condition may be employed toreduce the size of the pellets. In one example wherein milling isemployed, the pellets are ground in a bead mill at a temperature that isabove room temperature, such as at greater than or equal to about 40°C.—e.g., greater than or equal to about 50° C., about 60° C., about 70°C., about 80° C., about 90° C., about 100° C., or higher. Othertemperature values are also possible. In one example wherein milling isemployed, the pellets are ground in a bead mill for a period of lessthan or equal to about 20 hours—e.g., less than or equal to about 18hours, about 16 hours, about 14 hours, about 12 hours, about 10 hours,about 8 hours, about 6 hours, or shorter. In one example, the millingtime is between about 6 hours and about 14 hours—e.g., between about 8hours and about 12 hours, etc. Other milling/grinding times are alsopossible. The resultant ground particles may be any of theaforedescribed ink particles. For example, these ink particles may bespherical, or almost spherical. These particles may have any of thediameters described herein for ink particles.

As described above, the ink particles fabricated may be combined withother constituents to form an ink composition. In one example, the inkparticles are charged before being incorporated with other inkcomposition constituents (e.g., carrier fluid) into a toner. In anotherexample, the ink particles are charged by being co-existing with atleast one charger director in the ink composition. The ink compositionmay then be employed in a variety of applications. For example, the inkcomposition may be printed onto a substrate. Any suitable printingtechnique may be employed. For example, the printing may be digitalprinting. The digital printing may be, for example, LEP.

During the printing process, at least some of the ink particles mayconnect to one another as the liquid carrier fluid and/or the polymerresin of the ink particles dries up (or solidifies). The connection maytake the form of the ink particles fused together to form particleclusters; the fusing is described further below. The printing conditionsmay vary depending on the printing process. For example, the printingprocess may involve digitally pressing the ink composition over asubstrate. The digital pressing may be carried out at a temperatureabove room temperature to facilitate fusing of the ink particles and/ordrying of the carrier fluid and/or polymeric resin (of the inkparticles). In one example, the pressing temperature is greater than orequal to about 40° C.—e.g., greater than or equal to about 50° C., about60° C., about 70° C., about 80° C., about 90° C., about 100° C., about120° C., about 140° C., about 160° C., about 180° C., about 200° C., orhigher. Other temperature values are also possible. During digitalpressing, the carrier fluid dries up, and, as a result, the ink partiesmay be fused to create a three-dimensional structure, such as one ofthose described further below.

Printed Ink Composition

The ink composition described herein may be printed to form a printedink composition. The printed ink composition may be in the form of alayer disposed over a print substrate. The ink composition may be any ofthose described herein. In one example of the printed ink composition,the non-polar polymer is no longer a fluid (as in the carrier fluid) andinstead is a solidified polymer. The printing may refer toelectrophotographic printing, such as LEP. The print substrate may referto any material suitable for an ink composition to be disposed upon, andthe printed ink composition may be used to display a variety of formsand/or images, including text, graphics, characters, images, orphotographs. A print substrate may comprise vinyl media, cellulose-basedpaper media, various cloth materials, polymeric materials (examples ofwhich include polyester white film or polyester transparent film),photopaper (examples of which include polyethylene or polypropyleneextruded on one or both sides of paper), metals, ceramics, glass, ormixtures or composites thereof. In one example, the print substrate is apaper, including at least one sheet of paper, a roll of paper, etc.

The printed ink layer may have any suitable thickness. In one example,the thickness is large enough to accommodate a sufficient number ofcavities present in the printed ink composition for the printed inkcomposition to have a desirable opacity. For example, the layercomprising the printed composition may have a thickness that is greaterthan or equal to about 2 μm—e.g., greater than or equal to about 3 μm,about 4 μm, about 5 μm, about 6 μm, about 7 μm, about 8 μm, about 9 μm,about 10 μm, or larger. In one example, the layer thickness is betweenabout 2 μm and about 6 μm—e.g., between 3 μm and about 5 μm, etc. Theprinted ink composition may have a different microstructure than doesthe ink composition before being printed. As described further below,the ink composition described herein may provide certain characteristicsto the printed ink composition after printing.

In at least some examples, the tackifier may form an interface, or aninterfacial layer relatively thin (as compared to the overall printedink composition) between the printed ink composition and the substrate.The interfacial layer may be still a part of the printed inkcomposition. In one example, the interfacial layer is in the inkcomposition adjacent to the substrate.

Non-Limiting Working Examples Example 1

Two tackifiers were investigated in this Example: Regalite™ S5100 fromEastman Chemical Company, USA (“Regalite S”) and Nures™ TP 100 fromNewport Industries, USA (“TP100”). Each tackifier was dissolved inIsopar® (1-5 wt % on liquids) and added to ink compositions to createink composition samples. The base of the ink composition is HP Indigo'sElectroink® 4.5 (“EI4.5”). Electroink® 4.5 without any tackifier wasused as the negative control (Ref). The resin system of the inkcomposition investigated in this Example contained Nucrel™ 925, Nucrel™2805, and Bynel 2022™. The charge director employed in this Example isan SCD, which includes a sulfosuccinate salt. All tests were carried outusing HP's 7000 Indigo Presses, Hewlett-Packard Company, USA.

All of the ink composition samples were investigated with four differentsubstrates—Euroart™ (by Sappi of USA), UPM (by the Biofore Company,USA), FortuneMatte™ (by New Page of USA), and Soperset™ (by Soperset,USA).

FIGS. 2A-2D show the peeling test results for the ink compositions onthe four different substrates (A: Euroart; B: UPM; C: Fortune Matte; andD: Soperset). As shown in FIGS. 2A-2D, all ink composition samples withtackifiers showed significant better results in peeling than thereference ink composition (Ref) (without any tackifiers). The contrastin the peeling test results is particularly evidenced in the magenta inkwith different coverage percentage of two tackifiers (Regalite S andTP100), as compared to the Ref sample. Although both Regalite S and TP100 containing samples showed better results than the Ref sample in allfour substrates, TP100 showed better results than the Regalite S samplesin all four substrates. Not to be bound by any theory, but thedifference may be due to the presence of polar groups in TP100, whichincreases the adhesion to the substrate and rejection from the blanket.In fact, the paper was torn in the Soperset substrate because of thevery strong tackiness.

Furthermore, in a separate test, these tackifier materials wereevaluated in three different ink formulations:

1) Nucrel™ 960/ACLYN™ 201 based with a NCD, which includes a combinationof lecithin and sulfonate salts.

2) Nucrel™ 960/ACLYN™ 201 based with SCD, which includes asulfosuccinate salt.

3) Nucrel 925™, Nucrel 2805™, and Bynel 2022™ based ink with SCD, whichincludes a sulfosuccinate salt.

FIGS. 3A-3D show the test results. In all the test ink formulations, theobtained peeling results showed better results than the referencesample. As shown in FIGS. 3A-3D, the increase in adhesion issignificant, particularly seen in the peeling test results of Regalite Swithin Nucrel™ 960/ACLYN™ 201 based ink composition with an NCDcontaining a combination of lecithin and sulfonate salts.

In sum, the tackifiers investigated in this Example were found to enablebetter adhesion of the printed film (ink composition) to all of thesubstrates investigated than a sample without a tackifier. Specifically,these materials increased adhesion of the dried image to the substratewith better peeling results and increasing media gamut for use with LEP.Also, the addition of the tackifiers achieved desirable peeling resultswithout degrading the transfer of the image from the blanket tosubstrate.

Example 2

The ink transfer from a blanket to the substrate was investigated inthis Example. During LEP, the developed image was transferred from thePIP to the blanket (intermediate transfer media, or “ITM”). On theblanket, the image was melted and fused under heating lamps while thecarrier liquid was evaporated. In the next phase the image film wastransferred to the substrate (T2). All tests were carried out using HP's7000 Indigo Presses, Hewlett-Packard Company, USA.

The effects of incorporating tackifiers into LEP ink compositions wereinvestigated in this Example. Two tackifiers were investigated in thisExample: Regalite™ S5100 from Eastman Chemical Company, USA (“RegaliteS”) and Nures™ TP 100 from Newport Industries, USA (“TP100”). Eachtackifier was dissolved in Isopar® (1-5 wt % on liquids) and added tobase ink compositions to form ink samples. The tackifiers wereintroduced into two ink systems:

(1) EI4.5 based ink composition with an SCD—Nucrel™ 960/ACLYN™ 201 basedwith an SCD, which includes a sulfosuccinate salt.

(2) HP Indigo ink composition having a resin system containing Nucrel925™, Nucrel 2805™, and Bynel 2022™ based ink with an SCD, whichincludes a sulfosuccinate salt.

It was observed that in both ink systems, the introduction of TP100 as atackifier resulted in continuous ink transfer from blanket to substrate.The result was particularly surprising for the ink system (2), as theresin system used therein is known to exhibit transferability challengesin some instances.

Not to be bound by any particular theory, but the introduction oftackifier may have enhanced the ink transfer, particularly in T2, asfollows:

1) The tackifier that bleeds out of the ink layer on the side of theblanket gradually forms a film on the blanket. The tackifier wets theblanket's surface, but does not adhere to it. It is believed that thisfilm acts as a barrier interfering with ink-blanket adhesion, and/or asa layer that enhances transfer as a “lubricant,” by splitting during T2.

2) The tackifier that bleeds out of the ink layer on the opposite sideof the ink film functions as a glue between the ink and the substrateenhances ink tackiness to the substrate and further facilitating T2.

Support for 1) is shown in FIGS. 4A-4B. FIGS. 4A and 4B show that theRegalite S tackifier wetted used blankets and formed a film—FIG. 4Ashows a new blanket and FIG. 4B shows a used blanket. It was observedthat the blankets became less hydrophobic with use, enabling filmforming of relatively polar tackifier materials.

FIG. 5 shows background on blanket (“BOB”) accumulated ink remnants onblanket in non-image areas) vs. stages in a short press test (20K imprun). The test was conducted to measure quantitative BOB and backgroundon print (“BOP”) outputs via X-RITE ISIS (OD-measuring scanner) andautomatic analysis through Excel. The output parameters included BOBlevels per area, BOP levels per area, total background transferred toblanket, % background that remained on blanket, cleanability (i.e.,number of cleaner pages to clean BOB, normalized by BOB level, andblanket memories (solid K, small dots). The types of blanket “histories”obtained included constant background—areas where no images are everprinted; areas printed for 1k when the blanket was fresh, and notprinted again; and areas printed for 1k and not printed for 1k. The

Each printed area divides into 5 possible solid images: 1^(st) sep,2^(nd) sep, 3^(rd) sep, 2^(nd)+3^(rd), all 3. Specifically,

Stages 1-2: Install ink & test blanket

Stage 3: 1× Color Adjust

Stages 4-10: 7× BOB+BOP

Stage 11: 3× Color Adjust

Stages 12-17: 6× BOB+BOP

Stage 18: 3× Color Adjust

Stages 19-24: 6× BOB+BOP

As shown in the figure, while printing with hard-resins-based inkwithout tackifier, BOB (ink accumulation) increased during the testuntil the blanket was unrecoverable and needed to be replaced at stage10. The two curves representing hard resins based ink with tackifierswere obtained with two different blankets and show shows that with atackifier as part of the ink system, BOB dropped close to zero and waseven better than the reference. The ink system (1) (the one with Nucrel™960/ACLYN™ 201 resins) is labelled “Ref. Ink”).

FIGS. 6A-6B show optical images of yellow cleaner pages printed at 24stages in order to clean and recover the blanket. FIG. 6A shows acleaner page printed with hard resins based ink without a tackifier.FIG. 6B shows a cleaner page printed with the same ink that shown inFIG. 6A but with a tackifier (TP100). Both cleaner Pages were printedafter the same blanket history, as the same stage of the test. The inkwith no tackifier failed at stage 12 and blanket did not survive (FIG.6A). By contrast, the cleaner page printed with TP100 had no visible inkremnants on it, showing that no ink remained on blanket and that secondtransfer met satisfaction.

In sum, the tackifiers were found to enhance ink transfer from blanketto substrate. Particularly, the incorporation of a tackifier allows useof high-durability ink and desired charge director, overcomingadhesion-transferability trade-off often faced by these high-durabilityinks. The tackifier dissolved in the carrier fluid (Isopar®) andperformed a dual task of decreasing ink adhesion to the blanket andincreasing ink affinity to the substrate, allowing continuous full inktransfer to the substrate. Also, it is believed that the thininterfacial layer film produced by the tackifier on the blanket surfacemay protect the blanket and avoid ink accumulation on it.

Additional Notes

It should be appreciated that all combinations of the foregoing concepts(provided such concepts are not mutually inconsistent) are contemplatedas being part of the inventive subject matter disclosed herein. Inparticular, all combinations of claimed subject matter appearing at theend of this disclosure are contemplated as being part of the inventivesubject matter disclosed herein. It should also be appreciated thatterminology explicitly employed herein that also may appear in anydisclosure incorporated by reference should be accorded a meaning mostconsistent with the particular concepts disclosed herein.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. Such a range format is used merelyfor convenience and brevity and thus should be interpreted flexibly toinclude not only the numerical values explicitly recited as the limitsof the range, but also to include all the individual numerical values orsub-ranges encompassed within that range as if each numerical value andsub-range is explicitly recited. As an illustration, a numerical rangeof “1 weight % (wt %) to 5 wt %” should be interpreted to include notonly the explicitly recited values of 1 wt % to 5 wt %, but also includeindividual values and sub-ranges within the indicated range. Thus,included in this numerical range are individual values, such as 2, 3.5,and 4, and sub-ranges, such as from 1-3, from 2-4, and from 3-5, etc.This same principle applies to ranges reciting only one numerical value.Furthermore, such an interpretation should apply regardless of thebreadth of the range or the characteristics being described.

In this disclosure, including the claims, all transitional phrases suchas “comprising,” “including,” “carrying,” “having,” “containing,”“involving,” “holding,” “composed of,” and the like are to be understoodto be open-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, § 2111.03.

What is claimed:
 1. A liquid electrophotographic ink composition, comprising: a charge director; a non-polar carrier fluid comprising a polymer; and ink particles each comprising a polymeric resin and a pigment dispersed in the resin; and a tackifier.
 2. The liquid electrophotographic ink composition of claim 1, wherein the charge director comprises at least one of a lecithin, a sulfonate salt, and a sulfosuccinate salt.
 3. The liquid electrophotographic ink composition of claim 1, wherein the tackifier comprises a polymer having a molecular weight Mn of between about 600 and about
 1000. 4. The liquid electrophotographic ink composition of claim 1, wherein the tackifier has a softening temperature of about 100° C.
 5. The liquid electrophotographic ink composition of claim 1, wherein the tackifier dissolves completely in an isoparaffin.
 6. The liquid electrophotographic ink composition of claim 1, wherein the tackifier comprises a hydrocarbon having a polar acid group.
 7. The liquid electrophotographic ink composition of claim 1, wherein the tackifier comprises at least one of a hydrocarbon resin, a hydrogenated hydrocarbon resin, a dimerized acid rosin, a terpene phenolic resin, an abietic acid, a rosin ester, and a polyterpene.
 8. The liquid electrophotographic ink composition of claim 1, wherein the tackifier comprises a dimerized acid rosin.
 9. The liquid electrophotographic ink composition of claim 1, wherein the polymeric resin comprises a copolymer of ethylene and methacrylic acid.
 10. A method of manufacturing a liquid electrophotographic ink composition, the method comprising: dissolving a tackifier in a non-polar carrier fluid comprising a polymer to form a mixture; combining the mixture with a charge director and ink particles each comprising a polymeric resin and a pigment dispersed in the resin to form the liquid electrophotographic ink composition.
 11. The method of claim 10, further comprising printing the liquid electrophotographic ink composition, the printing comprising: disposing the liquid electrophotographic ink composition over a portion of a substrate; and drying the disposed liquid electrophotographic ink composition to form an image over the portion.
 12. The method of claim 10, wherein the tackifier is disposed in the non-polar carrier fluid at between about 1% and about 5% by weight of the fluid.
 13. The method of claim 10, wherein the tackifier comprises at least one of a hydrocarbon resin, a hydrogenated hydrocarbon resin, a dimerized acid rosin, a terpene phenolic resin, an abietic acid, a rosin ester, and a polyterpene
 14. An article, comprising: a substrate; an electrophotographic ink composition printed over at least a portion of the substrate, the electrophotographic ink composition comprising: a charge director; a non-polar polymer comprising an isoparaffin; ink particles each comprising a polymeric resin and a pigment dispersed in the resin; and a tackifier.
 15. The article of claim 14, wherein the tackifier is in an interfacial layer of the printed ink composition adjacent to the substrate. 